In a turbocharger which is used in an engine for vehicles, etc., exhaust gas from the engine, adopted is the configuration in which exhaust gas from the engine fills a scroll formed in a turbine housing, and passes through a plurality of nozzle vanes provided on an inner circumferential side of the scroll to act on a turbine rotor provided on an inner circumferential side of the plurality of nozzle vanes.
The nozzle vanes are incorporated in a variable nozzle mechanism in which an opening angle (a vane angle) in an exhaust gas passage formed between two annular plates can be changed by an actuator.
By this variable nozzle mechanism, opening degrees of the nozzle vanes are changed in accordance with the rotation speed of the engine and hence, the flow rate of the exhaust gas flowing in the exhaust gas passage between the two plates changes, thereby changing the rotation speed of the turbine wheel.
For instance, to accelerate the engine by increasing the rotation speed of the engine from the state where the engine rotation speed is in a low speed range, it is necessary to increase the rotation speed of the turbine wheel by narrowing a passage of the exhaust gas to the state where the opening degree of the nozzle vanes is almost full-closed to raise the flow rate of the exhaust gas.
A stopper structure is need for this type of regulation and adjusting of the opening angle on the full-close side of the nozzle vane.
As the conventional stopper structure for regulating the opening degree of the nozzle vane in the turbocharger, there is a stopper structure illustrated in FIG. 8. This stopper structure for regulating and adjusting the opening degree of the nozzle vane is provided in a bearing housing that rotatably supports a rotation shaft of the turbine wheel constituting a turbocharger.
In FIG. 8, a turbocharger 100 comprises a turbine housing 102 for rotatably accommodating the turbine wheel, a bearing housing 103 attached to the turbine housing 102 and rotatably supporting the rotation shaft of the turbine wheel, and a variable nozzle mechanism 105 for adjusting a flow rate of the exhaust gas entering the turbine wheel by means of a plurality of nozzle vanes.
The variable nozzle mechanism 105 comprises a lever 112 attached to a support 111 so as to adjust the opening degrees of the nozzle vanes collectively, a connection mechanism 114 connected to an end of the lever 112 via a pin 113, an actuator 117 comprising a rod 116 connected to the connection mechanism 114, an extension part 121 integrally formed with the bearing housing 102 to regulate a swing angle of the lever 112, a stopper bolt 122 screwed in this extension part 121, and a rock nut 123 for fixing the stopper bolt 122 to the extension part 121.
The stopper bolt 122 works in the following manner. When the actuator 117 operates and the rod 116 is pulled down obliquely toward a right bottom hand in the drawing, the connection mechanism 114 moves down obliquely toward the right hand side in the drawing and the lever 112 connected to the connection mechanism 114 swings clockwise about the support 111, and the lever 112 comes in contact with a tip of the stopper bolt 122 to regulate further swinging of the lever 112. In other words, the opening degree of the nozzle vanes on the full-close side is regulated.
The opening degree of the nozzle vane on the full-close side can be adjusted by loosening the locknut 123, turning the stopper bolt 122, and advancing or retreating the tip 122a of the stopper bolt 122 with respect to the extension part 121. As a result, the swing angle of the lever 122 with respect to a point where the stopper bolt 122 contacts the tip 122a changes, whereby to change the opening degree of the nozzle vane on the full-close side.
There is also a turbocharger provided with a synchronization mechanism for changing an opening degree of a plurality of nozzle vanes in synchronized manner (see Patent Document 1, for instance).
According to FIG. 1 of Patent Document 1, a synchronization mechanism 6 for rotating a plurality of nozzle vanes synchronously is provided in a turbocharger 1. The synchronization mechanism 6 comprises an actuator 70 serving as its drive source.